Nanofibers Nanofibers Edited by Ashok Kumar Intech IV Published by Intech Intech Olajnica 19/2, 32000 Vukovar, Croatia Abstracting and non-profit use of the material is permitted with credit to the source Statements and opinions expressed in the chapters are these of the individual contributors and not necessarily those of the editors or publisher No responsibility is accepted for the accuracy of information contained in the published articles Publisher assumes no responsibility liability for any damage or injury to persons or property arising out of the use of any materials, instructions, methods or ideas contained inside After this work has been published by the Intech, authors have the right to republish it, in whole or part, in any publication of which they are an author or editor, and the make other personal use of the work © 2010 Intech Free online edition of this book you can find under www.sciyo.com Additional copies can be obtained from: publication@sciyo.com First published February 2010 Printed in India Technical Editor: Teodora Smiljanic Cover designed by Dino Smrekar Nanofibers, Edited by Ashok Kumar p cm ISBN 978-953-7619-86-2 Preface “There's Plenty of Room at the Bottom” ⎯ this was the title of the lecture, Prof Richard Feynman delivered at California Institute of Technology on December 29, 1959 at an American Physical Society meeting He considered the possibility to manipulate matter on an atomic scale Indeed, the design and controllable synthesis of nanomaterials have attracted much attention because of their distinctive geometries, and novel physical and chemical properties For the last two decades nano-scaled materials in the form of nanofibers, nanoparticles, nanotubes, nanoclays, nanorods, nanodisks, nanoribbons, nanowhiskers etc have been investigated with increased interest due to their enormous advantages, such as large surface area and active surface sites Among all nanostructures, nanofibers have attracted tremendous interest in nanotechnology and biomedical engineering owing to the ease of controllable production processes, low pore size and superior mechanical properties for a range of applications in diverse areas such as catalysis, sensors, medicine, pharmacy, drug delivery, tissue engineering, filtration, textile, adhesive, aerospace, capacitors, transistors, battery separators, energy storage, fuel cells, information technology, photonic structures and flat panel displays, just to mention a few Nanofibers are continuous filaments of generally less than about 1000 nm diameters Nanofibers of a variety of cellulose and non-cellulose based materials can be produced by a variety of techniques such as phase separation, self assembly, drawing, melt fibrillation, template synthesis, electro-spinning, and solution spinning They reduce the handling problems mostly associated with the nanoparticles Nanoparticles can agglomerate and form clusters, whereas nanofibers form a mesh that stays intact even after regeneration The present book is a result of contributions of experts from international scientific community working in different areas and types of nanofibers The book thoroughly covers latest topics on different varieties of nanofibers It provides an up-to-date insightful coverage to the synthesis, characterization, functional properties and potential device applications of nanofibers in specialized areas Based on the thematic topics, it contains the following chapters: VI Chapter 1: Carbon Nanofibers as Macro-structured Catalytic Support gives an overview of the synthesis of carbon nanofibers and their efficient applications in different catalytic reactions Chapter 2: Nanofiber Reinforced Composite Polymer Electrolyte Membranes deals with the enhancement of ionic conductivity of poly(vinylidene fluoride hexafluoropropylene) based composite polymer electrolyte membranes due to addition of dedoped polyaniline nanofibers as insulating fillers Chapter 3: Nanoreinforced Adhesives reviews the polymer nanocomposites manufactured from an effective dispersion of nanofillers (nanoclays, carbon nanotubes or nanofibers, inorganic nanoparticles etc) into a polymeric matrix (thermoplastic or thermosetting) for generating new multifunctional materials with improved mechanical, physical and chemical properties These nanoreinforced polymer composites have efficient application as adhesive Chapter 4: Fabrication of Bio-nanocomposite Nanofibers Mimicking the Mineralized Hard Tissues via Electrospinning Process describes electrospinning as a promising approach for fabrication of hydroxyapatite nanocrystals based bio nanocomposite fibers as hard tissue (bone and dentin) replacement and coating implants since they resemble to the nanostructure of living bone from the physiochemical point of view Chapter 5: Diversity of Nanofibers from Electrospinning: from Graphitic Carbons to Ternary Oxides discusses the electrospinning technique for synthesis of nanofibers and microfibers from graphitic carbon, binary, ternary and more complex oxides Chapter 6: Preparation of Functionalized Nanofibers and Their Applications provides an overview of the synthesis of functionalized nanofibers by electrospinning, their properties, theories and applications in energy storage devices, biomedical engineering and photocatalysis Chapter 7: Keratin-based Nanofibers deals with the extraction of keratin from wool and electro spinning of keratin-based blends with high molecular weight polymers like poly(ethylene-oxide), fibroin and polyamide for biomedical applications such as tissue engineering and medical textiles and active filtration of air Chapter 8: In Situ Probing of Oxygen-containing Groups on Acid-treated Carbon Nanofibers using Aromatic Molecules reports in situ fluorescence measurements using oxygen-containing aromatic probe molecules for studying the physicochemical properties on the carbon nanofibers surface The relationship between the carbon nanofiber dispersion throughout the solution of the probe molecules and their adsorption onto the carbon nanofibers has been discussed by analyzing the UV-visible and fluorescence spectra of the suspension containing the probe molecules and the untreated or acid-treated carbon nanofibers Chapter 9: Preparation of Cellulose-based Nanofibers Using Electrospinning describes the preparation of ethyl-cellulose and hydroxypropyl methylcellulose nanofibers using electro spinning technique Effect of polymer concentration, tip-target distance, solution flow rate, and applied voltage on the morphology of nanofibers is also emphasized Chapter 10: Nanofibrous Scaffolds of Bio-polyesters: In vitro and In vivo Characterizations and Tissue Response aims to prepare bio-polyesters by electro spinning for fabricating tissue-engineering scaffold with enhanced mechanical properties, bioabsorption and biocompatibility Its performance as a nanofibrous scaffold for tissue engineering was compared with electrospun homopolymers All of these nanofibrous scaffolds were implanted subcutaneously in rats to evaluate their tissue response VII Chapter 11 Photocatalyst Nanofibers Obtained by Calcination of Organic-Inorganic Hybrids depicts the synthesis of TiO2 – PVA organic-inorganic hybrids using electro spinning followed by calcinations The hybrid nanofibers are used as photocatalyst in degradation of Methylene blue under white light irradiation Chapter 12: Electrochemical and Adsorption Properties of Catalytically Formed Carbon Nanofibers describes the synthesis of carbon nanofibers by Catalytic Chemical Vapour Deposition(CCVD) method The electrochemical, adsorption and sensing properties of the fibers is also briefed Chapter 13: Synthesis of Carbon Nanofibers by a Glow-arc Discharge deals with the growth of carbon nanofibers by a glow-arc HF discharge These nanofibers are used as toxic gas absorber Chapter 14: Morphology and Dispersion of Pristine and Modified Carbon Nanofibers in Water focuses on dispersion of untreated and acid-treated carbon nanofibers suspended in water The morphology and dispersion of solubilized carbon nanofibers and dispersion of plasma-treated carbon nanofibers has been studied Chapter 15: Non-Catalytic, Low-Temperature Synthesis of Carbon Nanofibers by Plasma-Enhanced Chemical Vapor Deposition describes the non-catalytic, low temperature synthesis of carbon nanofibers by using DC plasma-enhanced chemical vapor deposition system and microwave plasma-enhanced chemical vapor deposition system, reaction mechanisms and growth models and comparison of properties of carbon nanofibers synthesized by the two systems Chapter 16: Carbon Nanotubes Reinforced Electrospun Polymer Nanofibers Synthesis of Alumina Nanofibers and Composites discusses the incorporation of carbon nanotubes into polymer nanofibers by electrospinning technique Some significant property changes and applications are also briefed A brief description on carbon nanotubes, its properties and composites are given It also gives an overview of the electrospinning technique and electrospun nanofibers Chapter 17: On the Electron Transport in Conducting Polymer Nanofibers highlights the current understanding of the electron conduction mechanisms in conducting polymer nanofibers Chapter 18: Spectroscopy of Polyaniline Nanofibers examines the vibrational Raman spectroscopic studies of polyaniline nanofibers synthesized by interfacial polymerization and soft miceller templates Chapter 19: Fabrication of Ceramic Nanofibers Using Atrane Precursor provides solgel and electro spinning approach for synthesis of zirconia nanofibers from its inexpensive and moisture-stable zirconatrane precursor The morphological and thermal properties of zirconia nanofibers have been studied Chapter 20: Organic Fluorescent Nanofibers and Sub-micrometer Rods: Interest of a Solvent-exchange Preparation Method describes the photo physical behavior and design of fluorescent nanofibers An overview of the different types of fluorescent nanofibers bionanofibers, dendrimer nanofibers and nanofibers based on berberine ion pairs, coumarin series and low molecular weight fatty acids and their preparation methods are presented here Chapter 21: Synthesis of Alumina Nanofibers and Composites covers the different chemical and physical methods for synthesis of alumina nanofibers The effect of alumina nanofibers on different polymers, inorganic and carbon substrates is also reviewed VIII Chapter 22: Core-Shell Nanofibers: Nano Channel and Capsule by Coaxial Electrospinning deals with the synthesis of nanochannel, core-shell nano-capsule and tubular nanostructures of various organic or inorganic materials by coaxial electrospinning technique Nanoencapsulation of stimulating responsive materials into core-shell nanofibers and their functional devices applications have also been discussed in detail We hope that this book will prove to be timely and thought provoking and will serve as a valuable reference for researchers working in different areas of nanofibers Special thanks go to the authors for their valuable contributions Editor Ashok Kumar Department of Physics, Tezpur University, Tezpur784028, Assam India Contents Preface Carbon Nanofibers as Macro-structured Catalytic Support V 001 Ricardo Vieira Nanofiber Reinforced Composite Polymer Electrolyte Membranes 013 A Kumar and M Deka Nanoreinforced Adhesives 039 Silvia G Prolongo, María R Gude and Alejandro Ureña Fabrication of Bio-nanocomposite Nanofibers Mimicking the Mineralized Hard Tissues via Electrospinning Process 069 Gyeong-Man Kim Diversity of Nanofibers from Electrospinning: from Graphitic Carbons to Ternary Oxides 089 Yu Wang, Idalia Ramos and Jorge J Santiago-Aviles Preparation of Functionalized Nanofibers and Their Applications 121 Young-Seak Lee and Ji Sun Im Keratin-based Nanofibres Claudio Tonin, Annalisa Aluigi, Alessio Varesano and Claudia Vineis 139 X In Situ Probing of Oxygen-containing Groups on Acid-treated Carbon Nanofibers using Aromatic Molecules 159 Hiromasa Nishikiori, Satoshi Kubota, Nobuaki Tanaka, Morinobu Endo, and Tsuneo Fujii Preparation of Cellulose-based Nanofibers Using Electrospinning 179 Youn-Mook Lim, Hui-Jeong Gwon, Joon Pyo Jeun and Young-Chang Nho 10 Nanofibrous Scaffolds of Bio-polyesters: In Vitro and In Vivo Characterizations and Tissue Response 189 Hui Ying Tang, Daisuke Ishii, Kumar Sudesh, Tetsuji Yamaoka and Tadahisa Iwata 11 Photocatalyst Nanofibers Obtained by Calcination of Organic-Inorganic Hybrids 213 Koji Nakane and Nobuo Ogata 12 Electrochemical and Adsorption Properties of Catalytically Formed Carbon Nanofibers 227 Liliana Olenic, Stela Pruneanu, Valer Almasan and Alexandru R Biris 13 Synthesis of Carbon Nanofibers by a Glow-arc Discharge 253 Marquidia Pacheco, Joel Pacheco and Ricardo Valdivia 14 Morphology and Dispersion of Pristine and Modified Carbon Nanofibers in Water 269 Jian Zhao 15 Non-Catalytic, Low-Temperature Synthesis of Carbon Nanofibers by Plasma-Enhanced Chemical Vapor Deposition 295 Shinsuke Mori and Masaaki Suzuki 16 Carbon Nanotubes Reinforced Electrospun Polymer Nanofibres 309 Minoo Naebe, Tong Lin and Xungai Wang 17 On the Electron Transport in Conducting Polymer Nanofibers 329 Natalya A Zimbovskaya 18 Spectroscopy of Polyaniline Nanofibers 349 Gustavo M Do Nascimento 19 Fabrication of Ceramic Nanofibers Using Atrane Precursor Bussarin Ksapabutr and Manop Panapoy 367 424 Nanofibers Fig Schematic illustration of multi-channel fiber shaping proposed formation process for multi-channel tube (Here, a three-channel tube served as an example.) Two immiscible liquids with different properties are in the multi-fluidic compound electrospinning system The outer liquid is a multi-component solution, in which the content of volatile solvent is in the majority, while the inner paraffin oil is a nonvolatile liquid In the initial stage of electrospinning process that the compound fluid jet just leaves the spinneret, both outer and inner fluids are of cylinder shape according to the morphology of spinneret With bending and whipping of the liquid jet in air, the volume of outer fluid shrinks remarkably by the lose of solvent Then a dilemma emerge that either outer fluid or inner fluids must deform under the shrink pressure because the shrunk tube shell cannot hold the three cylinder inner fluids any more Thermodynamic analysis indicates that the deformation of inner fluids is favorable for the stability of system The interfacial tension of the outer and inner liquids is much smaller than outer liquid the surface tension of outer liquid (Adamson et al, 1997) The deformation of outer solution needs more energy than that of inner liquids To lower the total free energy of the compound fluid, the outer fluid is drained to surface through the liquid node and border film (called Plateau border) between three inner fluids by capillary suction When the Plateau border suction is counterbalanced by the disjoining pressure then reaches a mechanical equilibrium state, the border film between neighbouring inner fluid becomes flat (Exerowa et al, 1998; Höhler et al, 2005) With the drainage of outer fluid, the inner liquids evolve to three flabellate liquid columns Plateau’s law indicates that three angles between Plateau border are equal (120°) under thermodynamic equilibrium conditions, which agree well with the mutual angle of Y-shape inner ridge of three-channel nanotube Generally speaking, to lower the free energy of the compound fluid system, the inner fluids transform to flabellate shape under the shrinkage pressure of outer liquid and form multi-channel nanotube with multi-pointed star shape inner ridge ultimately The multi-fluidic compound-jet electrospinning technique breaks through the limit at two fluids system that could generate programmable multi-channel or multi-component 1D nanomaterials in an effective way 3.2 Mulit-channel nanofibers After an utmost control compound-jet electrospinning process and follow-up treatments (the inner channels of the tube correspond to the vacancy of the inner fluids after they were removed), Figure and Figure show the SEM images of the multi-channel fibers prepared by coaxial electrospinning The fibers have uniform, flat and smooth surface The side-view Core-Shell Nanofibers: Nano Channel and Capsule by Coaxial Electrospinning 425 was checked to expose the cross sections of the multi-channel fibers It can be clearly seen that most of tubes are of hollow structures with multi-cavum, circular and closed outer wall of the hollow tube The diameter distribution of the tubes is relative uniform with average value of 2.3 µm (in a sub-nano size) The inner diameter of the channels is around 100-500 nm size Decades nanometer walls made the compartment of the several cavums The through cavums form the nano-channels in the polymer or inorganic fibers and give the huge surface area The multi-furcate ridge embeds in the outer tube and exhibits an interesting mulit-pointed star “Y” or “X” shape, and the ridges partition the nanotubes into several flabellate parts Like a scaffold, the multi-furcate ridges support the hollow structure, and make the hollow structure have higher intensity Fig The cross section SEM images of hollow fibers with two, three, four and five channels The scale bars are 100 nm In Figure 6, nanotubes with two, three, four and five channels have been successfully fabricated by multi-channel coaxial electrospinning All of the multi-channel nanofibers show good fidelity to the corresponding spinneret With different inner fluid speed control of multi-fluidic compound-jet, one would fabricate the two or three channel nanofibers with different inner diameters That reveals the efficient controllability to construct multi-channel tube with different shapes in polymer nanofibers The multi-channel coaxial electrospinning 426 Nanofibers has good diversity It demonstrates that multi-channel coaxial electrospinning could fabricate all kinds of multi-channel nanofiber in theory Fig Schematic of the multichannel structure in biology, which show great means of multichannel fibers in bionics Materials delivery multichannel in lotus root a)-b), and multicavum structure for anti-cold in aves feather c)-d), and polar bear hair e)-h) Core-Shell Nanofibers: Nano Channel and Capsule by Coaxial Electrospinning 427 In application and biology, multichannel tubes or fibers have great importance and prospect Figure displays several typical examples of the multichannel structure in biology There are multichannel in lotus root for the materials delivery Multicavum structure in aves feather makes the feather ultra-light and high intensity And multicavum structure in polar bear hair makes it have prefect temperature keeping and anti-cold property (The infrared image of polar bear in Figure 7f shows that the heat energy losing only happens on the eyes, nose and ears, where are no or less hair covered parts.) High similarity with biological micro- or nanostructures and large areas, fast fabrication will give multi-channel fibers and multi-channel coaxial electrospinning wide prospects for research and application Compared with single channel, multi-channel structures may possess considerable advantages such as independent addressable channels, better mechanical stability, unique thermal properties and larger surface-to-volume area Furthermore, by replacing inner fluids with other functional molecular, multicore-shell nanofibers can be created and different components can be integrated in nanodomain without interaction Such nanofibers would have novel and improved properties that not exist in each component They might be promising candidates for a wide range of applications such as bionic super lightweight, thermo-insulated textiles, high efficiency catalysis, vessels for macro/nano fluidic devices in bioscience or lab-on-a-chip and multi-component drug delivery This general method could be readily expanded to many other materials Melt coaxial electrospinning and Nano-encapsulation and capsule in nanofibers Multiplicity, controllability and applicability are the aspect and prospects of nano-science and nano-technology At the same time for improving multiplicity and controllability, materials scientists pay great attention on the application of the new nano-technology or the new application of general nano-technology Following diversification development of responsive materials and nano-technology, the combination of various functional materials with nano structures are drawing much attention for the great prospect in smart materials and devices, which always can generate new materials with prominent functions (Gil et al, 2004; Lu et al, 2007) The core-shell nanomaterials give small capsule to encapsulate the responsive or functional materials And the coaxial electrospinning technique is an easy and fast process to build kinds of core-shell nanofibers In the fore part of this chapter, we have discussed coaxial electrospinning can perform good control, and fabricate core-shell and hollow nanofibers fast and simply In the coaxial electrospinning process of fabricating polymer nanofibers, the inner fluid and outer fluid should be delaminated and without mutual mixing, for example water and dichloromethane (DCM), to keep a clear interface between core and shell of the nanofibers However, for good conductivity and solubility, most good solvents for electrospinning are amphiphilic, for example dimethylformamide (DMF), dimethyl sulfoxide (DMSO), tetrahydrofuran (THF) and ethanol But as a fast process of electrospinning, if the outer fluid polymer solution was dry and the inner fluid was solidify before the mixture, the nice coreshell structure still can be bullied in the polymer nanofibers 4.1 Melt coaxial electrospinning In 2006, based on coaxial electrospinning, Prof Xia’s group made the first try and invented melt coaxial electrospinning to fabricated phase change materials encapsulation core-shell 428 Nanofibers nanofibers (McCann et al., 2006) They appended a heating system on the conventional coaxial electrospinning setup to provide a thermal atmosphere for the fluidic inner fluid The melt coaxial electrospinning experimental setup is shown in Figure The heating tape with a temperature controller device on the inner fluid syringe was used to keep the inner fluid molten and fluid Two syringe pumps were used to perform the utmost control of the inner fluid (melt hydrocarbon phase change materials) and outer fluid (PVP/Ti(OiPr)4 solution) respectively The two fluids met at the metallic needle spinneret, which was built to coaxial cannula Electrospinning relied on the use of a high-voltage electric field to draw a viscous droplet into an elongated jet Under high-voltage service, the liquid was pulled out from spinneret to fibers thinner and thinner In this process, the inner melt hydrocarbon phase change materials fluid froze rapidly, and the outer fluid polymer solution dried and solidified fast Fig Schematic of the melt coaxial electrospinning setup used for fabricating TiO2-PVP nanofibers loaded with hydrocarbon PCMs 2009, Dr Li and Prof Song made an improvement for the melt coaxial electrospinning (Li et al, 2009) The melt coaxial electrospinning experimental setup is shown in Figure In addition to the high voltage generator supply and the syringe pump controller, a whole thermal atmosphere heating system was build into the conventional coaxial electrospinning setup Two injectors with different diameter and needles constructed the outer and inner dopes loading setup In practice, the whole thermal atmosphere of loaded system was proved more propitiously to prevent the inner dope’s freeze by jamming of the needle (For low phase change temperature materials, an infrared lamp will be easier to supply a whole thermal atmosphere for the loaded system.) Keeping the inner inject materials (the phase change materials) fluid before it is spun out from spinneret should be treated with an Core-Shell Nanofibers: Nano Channel and Capsule by Coaxial Electrospinning 429 utmost care and control It is the key factor to keep the propitious encapsulation of phase change materials into the inner of the fibers and get the Phase Change Materials (PCMs)Polymer core-shell fibers with a high yield filling A dynamic instability resulted in whipping and stretching which was responsible for the attenuation of the jet into long fibers with ultrathin diameters Electrospinning was remarkably simple and versatile and capable of producing nano- and microscale fibers in large quantities Polymer solutions were predominantly used in this process, though composites, sol-gels, and surfactant-based solutions had also been included to fabricate nanofibers with a broad range of compositions, morphologies, and properties Fig The melt coaxial electrospining setup with a whole thermal atmosphere for the loaded system used for fabricating polymer nanofibers loaded with phase change materials 4.2 Nano-encapsulation and capsule in nanofibers 4.2.1 Phase change materials encapsulation in nanofibers Scanning electron microscopy (SEM) images and transmission electron microscopy (TEM) images can clearly recal the secondary nanostructures of the fibers electrospun with a melt coaxial spinneret Figure 11 shows the Octadecane@TiO2-PVP nanofibers electrospun with a melt coaxial spinneret by Prof Xia’s setup (Figure 8) The sheath consisted of a TiO2-PVP composite while the core was octadecane The core material was heated up to melt temperature for injection In Figure 10 (A) and (C) show the SEM images of the as-prepared fibers with different hydrocarbon materials loading, and (B) and (D) show the corresponding TEM images of the fibers after they have been soaked in hexane for 24 h to remove the hydrocarbon core Those fibers were 100-200 nm in average diameter The TEM images indicate that the octadecane formed spherical droplets or elongated, compartmentalized domains along the long axis of the fiber 430 Nanofibers Fig 10 Octadecane@TiO2-PVP nanofibers electrospun with a melt coaxial spinneret SEM images and TEM images of the nanofibers with 7% (A)-(B) and 45% (C)-(D) octadecane loading Fig 11 Tetradecanol@PMMA nanofibers electrospun with a melt coaxial spinneret SEM images of nanofibers in wide area (a) and side-view of core-shell nano- fiber lateral sections (b)-(c), and core-shell structure in TEM images (d) Figure 11 is the Tetradecanol@PMMA nanofibers electrospun with a melt coaxial spinneret by Prof Song’s setup (Figure 9), which shows the actual loading state of core-shell nanofibers (No core-removing) The sheath consisted of optical transmission polymer Core-Shell Nanofibers: Nano Channel and Capsule by Coaxial Electrospinning 431 ploy(methyl methacrylate) (PMMA) while the core was 1-tetradecanol and phase transformation developer composite (CBT) Figure 11a indicates the SEM image of the fibers with smooth surface and 500 nm to μm average diameter In the side-view SEM image of Figure 11b and 11c, core-shell structure of nanofiber lateral sections was displayed TEM image in Figure 11d reveals the clear interface between 1-tetradecanol core and PMMA polymer shell, and 200 nm inner diameter and 500 nm outer diameter It is the actual core-shell nano-fibers Further more, it indicates that the core-material was encapsulated independently and phase separated from polymer matrix shell wall That will be the most important fact to keep the thermo-responsive, energy-storage and management properties of the phasetransformation 4.2.2 Stimulation chromic materials encapsulation in nanofibers As a kind of classic responsive material, phase change materials (PCMs) were attracted much attention for the phase transformation absolutely reversibility and good energy storage and management property (Muligan, et al., 1996; Zalba, et al, 2003) However, the fluidity of the phase change materials after melting made the PCMs hard to fix and stabilize, which limited the practical application It is necessary to stabilize PCMs in a solid matrix The melt coaxial electrospining just gives a suitable and ideal process and method to encapsulate and stabilize the PCMs into the nanomatrix of core-shell polymer fibers The core-shell structure gives the free space out of the polymer matrix for their phase change As illustrated in Figure 12, the PCMs were encapsulated and stabilized in the centre cavum, where it could perform the melt and crystallization independently and no interruption And with the nano-encapsulation, the fluidity of the melt PCMs will be utmost limited by the strong capillarity of the nanotubes While huge surface of nanofibers provide huge heat area when the temperature change, which should make a more sensitive thermo-responsive property of the PCMs It provides the new insight into the preparation of temperature sensors, calefactive materials with energy absorption, retention, and release Fig 12 Reversible phase transformation process in core-shell nanofiber of phase change materials Figure 13 displays the experiment for the capability of these PCM Octadecane@TiO2-PVP nanofibers to stabilize temperature A borosilicate glass vial was covered with a different insulation jacket, filled with quantitative 60 °C water and then allowed to cool in a °C environment The water temperature in the vial was measured using a thermal couple every 432 Nanofibers 30 s and recorded until it reached 20 °C Curve A was no insulation jacket on the glass vial; curve B and C was half and whole insulated with a mm thick layer of octadecane@TiO2PVP fibers sandwiched between Al foils on the vial; and curve D was the vial covered with an mm thick jacket of fiberglass fibers Supercooling of vial A was not observed in the temperature history curve for the PCM nanofibers And the fiberglass fibers were as effective as the PCM nanofibers in insulating the vial with a times thicker cover The PCM fibers cover had a temperature stabilization time (close to the melting point of octadecane) for It gave an evident energy release in the cooling process, which indicated a practical applicable energy storage and management character Fig 13 Demonstration of thermal insulation capability of octadecane@TiO2-PVP nanofibers, where cm3 of water at 60 °C was allowed to cool in a °C environment in glass vials covered with different insulation jackets Fig 14 Schematic of phase change thermochromic material CVL, bisphenol Ae and 1tetradecanol (CBT) thermochromism in the phase-change process Core-Shell Nanofibers: Nano Channel and Capsule by Coaxial Electrospinning 433 To realize more application, Dr Li and Prof Song introduced the thermochrom into the PCMs core-shell nanofibers They used the phase change thermochromic materials (PCTMs) to make an improvement to PCMs Displaying in Figure 14, PCTM system of crystal violet lactone (CVL) as dye and bisphenol A as developer mix in fatty alcohol or fatty acid was chosen (Burkinshaw, et al., 1998; Hirata, et al., 2006; MacLaren, et al., 2005) As a traditional PCTM, it has a simple component and stable thermochromic property, and the thermochromic temperature can be adjusted by changing fatty alcohol or fatty acid filling (Here, 1-Tetradecanol 37~ 39 °C PCM was chosen for the good prospect in intelligent senors and devices of body temperature materials.) And CVL, bisphenol A and 1-tetradecanol (the mixture system was abbreviated to CBT) were chosen as the inner loading material for the melt coaxial electrospinng Fig 15 a) DSC measurements cycle curve and b) Fluorescence spectra of the CBT-PMMA nanofibers at 10 °C and at 50 °C After successful encapsulation by melt coaxial electrospinng, (Figure 11) these CBT-core and PMMA-shell nanofiber non-woven materials show some excellent properties Figure 15 indicates the thermo-responsive property Differential scanning calorimetry (DSC) experiment gave the DSC cycle curve of CBT-PMMA fibers, which revealed an obvious absorption and release process in the DSC measurement cycle (Figure 15a) The acuate peak and vale of DSC cycle curve indicates that the CBT-PMMA core-shell nanofibers have a more sensitive phase-transformation behaviour than a bulk CBT mixture (McCann et al., 2006; Li et al, 2009) Figure 15b shows the fluorescence spectra below and beyond the phase change temperature At the freezing state of CBT at 10 °C, the fibers have strong fluorescent emission at 503 nm, which is the characteristic fluorescence of CVL in CBT system With temperature increased to 50 °C, the emission intensity of the fibers has a great decrease When temperature is decreased to 10 °C, the emission intensity was reverted again The fluorescent change of the fibers in the heating-cooling process showed the obvious thermochromism PMMA polymer was used as the out shell material to encapsulate the thermochromic material, due to its good optical transparent property, which always be used for organic glass Figure 16 displays the fluorescent signal and image under fluorescence microscope With UV light exciting, the CBT-PMMA nanofibers showed good green emission and got 434 Nanofibers clear fluorescence image That makes the encapsulation of fluorescence thermo-chromic materials in core-shell nanofibers have an insight into the thermo-responsive senor Fig 16 (a) Optical and (b) fluorescent images of CBT–PMMA nanofibers of fluorescence microscope Fig 17 The thermochromic cycle reversibility experiment of CBT-PMMA nanofibers’ film In each cycle, the fluoresecent emission at λ = 503 nm of the samples was monitored at 10 °C and 50 °C, respectively The thermochromic reversibility cycle experiments of the CBT-PMMA fibers film were investigated to check the responsive stability The fluidity after melting is the main limiting factor for the PCTMs practical application The encapsulation of PCTMs in micro/nano matrix to stabilize the PCTMs could solve the problem In Figure 17, ten heating-cooling cycles between 10-50 °C were performed, and the fluorescent maximal emission at 503 nm of the CBT-PMMA fibers film was monitored There was not any essential loss in fluorescent characteristics during the repeated thermochromism processes It proved that the CBTPMMA core-shell nanofibers showed good fluorescence thermochromic reversibility The encapsulation of CBT in PMMA nanofibers realizes the device and practical application of PCTMs CBT It has new insight into the preparation of temperature sensors with good Core-Shell Nanofibers: Nano Channel and Capsule by Coaxial Electrospinning 435 fluorescence signal, and body temperature calefactive materials with intelligent thermal energy absorbing, retaining and releasing Melt coaxial electrospinning is one good example to fabricate functional core-shell nanofiber materials By introducing different responsive or functional materials as the core and choosing adaptable polymer, we could accomplish the novel functionality and function modification Thus we could perform versatile modification and control to realize multifunction and diversification, for the multi-channel coaxial electrospinning example As the extension and development of coaxial electrospinning, melt coaxial electrospinning shows good application performance and controllability It indicates the generality of electrospinning for one-dimensional nanomaterials fabrication 4.2.3 Future of core-shell nanofibers: Multi-encapsulation and Multi-responsive materials Fig 18 SEM (a) and TEM (b) image of multichannel nanofibers, which could be loaded with different fluorescence materials, and colourful fluorescence images (c)-(e) of multiencapsulation core-shell nanofibers Diversification and integration is the pilot of the science research on philosophy And for the aspects and prospects of the new materials developing currently and future, the multifunctional, integrative and miniature devices researches are greatly and urgently expected At the same time for core-shell nanofibers, diversification and multifunction will be the main aspects in the future Coaxial electrospinning provides the flexible and facilitate method to construct and fabricate diversiform nano- or micro- encapsulation materials and core-shell nano- or micro- devices Figure 18 shows some primary research of the multi- 436 Nanofibers encapsulation and multi-responsive materials in the core-shell nanofibers by coaxial electrospinning In the cavums centre of the fibers, rhodamine B and fluorescein isothiocyanate (FITC) et al dyes were used as the core loading materials to make the multichannel stain Then, colourful fluorescence images of multi-loading integrative core-shell nanofibers were obtained as shown in Figure 18 (c)-(e) We could believe that: with more versatile responsive materials loading or encapsulation, one can obtain the more multifunction nanofibers materials by coaxial electrospinning Conclusion Compared with self-assembly of molecular building blocks or template printing et al methods, coaxial electrospinning can be used to prepare various organic or inorganic tubular nanostructures fast and facilely With better controlling, coaxial electrospinning can realize diversification and encapsulation of nanofibers with tubular or core-shell second nanostructures Multichannel nanotubes have ultra-large specific surface area, isolation nanostructure and continuous nanotube In core-shell nanofibers, as core, varied responsive materials were independently encapsulated into polymer-shell The materials were fixed and protected, but the responsive properties were kept With nano-space encapsulating and ultra-large specific surface area, the responsive core-shell nanofibers materials are more sensitive on stimuli-responsive properties These core-shell nanofibers or nanotubes have great applications in catalysis, fluidics, ptrification, separation, gas storage, energy conversion and storage, drug release, sensing, and environmental protection Creating and accurate controlling 1D nanomaterials with multicompartmental inner structures is still a great challenge It is believed that the core-shell nanofibers will give a wide space to scientists to show more creativity at the nano-channel and nano-encapsulation domain Acknowledgments The authors thank the Natural Science Foundation of China (NSFC), the Ministry of Science and Technology (MOST) of 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Microscope (SEM) (JEOL 6390 LV) The size of PAni nanofibers was determined by TEM (JEOL-TEM-100 CXII) 4.2 Results and discussion 4.2.1 TEM studies Fig 2 shows the TEM micrograph of PAni nanofibers From the figure it is observed that nanofiber is composed of randomly packed polymer chains As the PAni nanofibers are Fig 2 TEM micrograph of dedoped Pani nanofibers 21 Nanofiber Reinforced Composite Polymer... that of polymer electrolytes containing nanofibers This result confirms that the interfacial stability of the polymer electrolyte containing nanofibers is better than that of without nanofibers This can be attributed to the fact that when nanofiber is added passivation of polymer electrolyte due to reaction with electrode material decreases High aspect ratio (> 50) nanofibers get accumulated on the surface... outside of the composite by water added due the hydrophobicity of nanofibers (Figure 5B), letting the active sites exposed for a longer period of time Fig 5 (A) H2S conversion as a function of time on 15% NiS2/CNF catalyst at different temperatures (B) SEM micrograph of the particular mode of sulfur deposition on carbon nanofibers Carbon Nanofibers as Macro-structured Catalytic Support 7 3.4 Fuel cells... over carbon nanofibers based composite was about 30% higher than on carbon nanotubes powder support for reactions above 400°C Figure 7 shows the better performance of the carbon nanofibers based support, due to its opened structure, thus reducing the diffusion problems Fig 7 Curve of ammonia conversion in function of the temperature on the 5% Ru/CNF (○) and 5% Ru/CNT catalyst (□) Carbon Nanofibers. .. absence of ink-bottle pores and carbon nanofibers hydrophobicity 4 Conclusion In summary, macro-structured carbon nanofibers can be efficiently employed as a new class of catalyst support which exhibits a high catalytic activity along with peculiar product selectivity when compared to those observed using traditional catalysts The high catalytic performances of the carbon nanofibers based catalyst were mainly... Vieira, R (2008) Ammonia decomposition using carbon nanofibers composites as catalytic support of ruthenium Proceedings of III International Symposium on Carbon for Catalysis, pp 95, Fritz Haber Institute, November 2008, Berlin Carbon Nanofibers as Macro-structured Catalytic Support 11 Furtado, J L B (2009) Development of a new monolith catalyst based carbon nanofibers for produce clean fuel by Fischer-Tropsch... incorporating dedoped (insulating) polyaniline nanofibers instead of nanoparticles into P(VdF-HFP)(PC+DEC)-LiClO4 gel polymer electrolyte system and PEO-P(VdF-HFP)-LiClO4 blend electrolyte system The concentration of dedoped polyaniline nanofibers has been varied and its effects on ionic transport in both the systems have been investigated 3 Synthesis techniques of nanofibers 3.1 Electrospinning Electrospinning... effective compared to that of most bottom-up methods The nanofibers prepared from Electrospinning process are often uniform and continuous and do not require expensive purification unlike submicrometer diameter whiskers, inorganic nanorods and Fig 1 Shematic diagram of electrospinning setup 18 Nanofibers carbon nanotubes (Dzenis, 2004) Polymer nanofibers mats are being considered for use in composite ... nanofibers, (c) P(VdF-HFP), (d) P(VdF-HFP )-( PC+DEC)-LiClO 4-2 % dedoped polyaniline nanofibers, (e) P(VdF-HFP)(PC+DEC)-LiClO 4-4 % dedoped polyaniline nanofibers, (f) P(VdF-HFP )-( PC+DEC)-LiClO 4-6 ... polyaniline nanofibers, (g) P(VdF-HFP )-( PC+DEC)-LiClO 4-8 % dedoped polyaniline nanofibers, (h) P(VdF-HFP )-( PC+DEC)-LiClO 4-1 0 % dedoped polyaniline nanofibers composite polymer electrolyte systems 28 Nanofibers. .. of dopant (PPyp-TSA > CSA > HCl > FeCl3 > PSSA), PPy-p-TSA nanofibers showing the highest electrical conductivity of × 10 -2 S/cm P(VdF-HFP )-( PC+DEC)-LiClO4-Dedoped polyaniline nanofibers composite